1. Field of the Invention
The invention relates to a power transmission device having a switching mechanism that allows and interrupts transmission of power.
2. Description of the Related Art
Hybrid automobiles having an engine and a motor (electric motor) as drive sources have recently been developed. There are also hybrid automobiles in which a motor serving as a drive source is also used as a starter.
For example, Japanese Patent Application Publication No. 2006-137406 (JP-A-2006-137406) discloses a drive apparatus for a vehicle including an engine, a transmission driven via a torque converter, an intermediate output shaft transmitting rotation drive power to the torque converter, an electric motor having a rotor fixed to the outer circumferential side of the intermediate output shaft, and a clutch mechanism disposed between the crankshaft of the engine and the inner peripheral surface of the rotor. The clutch mechanism has a hub member having an outer wheel portion that rotates integrally with the crankshaft and a pair of clutch plates disposed on the outer periphery of the hub member and on the inner peripheral surface of the rotor and pressed by a plate spring. The clutch mechanism connects the crankshaft of the engine to the intermediate output shaft to enable the vehicle to run, and enables restart control that drives the crankshaft of the engine using the electric motor in a state in which no load is applied on the transmission side.
As described in JP-A-2006-137406, the rotation generated by the electric motor can be transmitted to the engine by engaging (connecting) the clutch by the plate spring and connecting the crankshaft of the engine to the intermediate output shaft. As a result, the electric motor can be used as a starter.
However, in the device described in JP-A-2006-137406, a spring with a large pushing load should be used as the plate spring in order to maintain the engaged state even when a large load is applied to the clutch. Therefore, a large plate spring should be used and the device is increased in size. Where a plate spring with a large pushing load is used, the spread of load increases and therefore a load required for switching between engagement and disengagement is difficult to control. Further, a load necessary to disengage the clutch also increases and the amount of energy used for disengagement rises. In other words, the amount of energy necessary for switching the power transmission paths increases.